PROJECT SUMMARY/ABSTRACT Mood disturbance and cognitive impairment during the postpartum period are common and serious problems in women's mental health. Early life stress, such as psychosocial stress during adolescence, increases the risk for postpartum emotional and cognitive problems in humans, including the development of postpartum mood disorders. Nonetheless, the biological mechanisms linking adolescent stress to postpartum emotional and cognitive abnormalities are not well understood. Our long-term goal is to examine how pre-partum life stress affects hormonal systems, neural function, and behaviors in the developmental trajectory from adolescence to the postpartum period and dissect the mechanisms from molecules to circuits and behavior. Human imaging studies have linked functional changes in the projections from the anterior insula (AI) to dorsal anterior cingulate cortex [dACC, homologous to the prelimbic cortex (PrL) in rodents] to postpartum behavioral changes. Elevated levels of glucocorticoids by disturbance of negative feedback of the hypothalamic-pituitary-adrenal axis during the postpartum period can alter neural function. To gain more biological insight into these points, we have built a novel platform to study the biological mechanisms underlying the effects of adolescent stress on postpartum emotional and cognitive behaviors in first-time mothers, based on the adolescent social isolation paradigm we have already published. Hence, our current objective is to test the hypothesis that adolescent stress, in conjunction with the stressful events of pregnancy/delivery, leads to deficits in postpartum behaviors related to mood and social cognition via glucocorticoid-mediated functional alterations of AI-PrL glutamatergic projections. To address this hypothesis, we will pursue the following specific aims: In Aim 1, we will examine the role of AI-PrL projections in adolescent stress-induced PrL dysfunction and behavioral deficits in adult postpartum mice using a combination of state-of-the-art techniques, including in vivo calcium imaging in conjunction with projection-specific neuronal manipulation in freely moving mice. In Aim 2, we will determine the role of glucocorticoid receptor (GR) in adolescent stress-induced PrL dysfunction and behavioral deficits in adult postpartum mice. In Aim 3, we will combine retrograde tracing and cell type-specific manipulation using the green fluorescent protein (GFP)-dependent Cre recombinase system to examine the causal role of GR-mediated AI-PrL glutamatergic projections in the PrL dysfunction and behavioral deficits in adult postpartum mice pre-exposed to adolescent isolation rearing. Our findings may provide biological insights into postpartum mood disturbance and cognitive impairment, which are highly prevalent and have deleterious effects not only on the mother, but also on the children and the rest of the family. These findings will have a broad impact on the well-being of women and children worldwide.